1. Field of the Invention
The present invention relates to a power generation control apparatus, for use in a motor vehicle (or vehicle), capable of controlling an output voltage of a vehicle generator (or vehicle alternator) to be mounted on the vehicle such as a passenger car and a truck.
2. Description of the Related Art
In the recent years, a motor vehicle (or vehicle) tends to decrease a rotation speed (or rotation number) of a vehicle engine (or engine) mounted thereon during the idling condition as low as possible in order to reduce its fuel consumption. However, when a rotation speed of the engine becomes low, the output torque of the engine becomes low indeed. Thereby, the variation of the driving torque for auxiliary devices such as a vehicle generator (or vehicle alternator), connected to the engine through a belt, greatly affects the stability of the rotation speed of the engine during its idling condition. In such a background, there is a conventional technique to provide a stable rotation speed of the engine, in which a generation torque of the vehicle generator is calculated based on an exciting current and a rotation speed of the vehicle generator, and the technique controls so that a change rate of the calculated generation torque of the vehicle generator does not exceed a predetermined value. For example, Japanese patent laid open publication number JP 2003-284257 discloses such a technique (see pages 3 to 6 and FIGS. 1 to 6).
However, although the conventional power generation control apparatus disclosed in JP 2003-284257 is capable of estimating the torque of the vehicle generator during a stable rotation speed of the vehicle generator, it is difficult to estimate an accurate torque of the vehicle generator during a varying rotation speed of the engine, and as a result, the conventional technique introduces the voltage drop of the output voltage of the vehicle generator more than necessary and it is thereby difficult to perform the optimum control of the exciting current flowing through the exciting winding. The reason why is as follows. During the varying rotation speed of the engine, an estimated output torque of the vehicle generator is different from an actual torque of the vehicle generator because an inertia torque caused by the moment of inertia of the vehicle generator itself is generated in direction to nullify the variation of the rotation speed of the engine.
The above conventional power generation control apparatus disclosed in JP 2003-284257 suppresses the exciting current in order to reduce the change rate of the torque of the vehicle generator and the output voltage of the vehicle generator is thereby dropped, and such a technique further decrease the output voltage because the estimated torque of the vehicle generator calculated becomes a large value, and the large value of the estimated torque further suppresses the amount of the exciting current because of not considering any inertia torque of the vehicle generator. Thus, the conventional technique involves such a drawback.